Reuse the logic from navigation exception.

Author: ilonatommy

src/Components/Endpoints/src/Rendering/EndpointHtmlRenderer.EventDispatch.cs

@@ -89,7 +89,7 @@ private void SetNotFoundResponse(object? sender, EventArgs args)
 
     private async Task OnNavigateTo(string uri)
     {
-        if (_httpContext.Response.HasStarted || _httpContext.Request.Method == HttpMethods.Post)
+        if (_httpContext.Response.HasStarted)
         {
             var defaultBufferSize = 16 * 1024;
             await using var writer = new HttpResponseStreamWriter(_httpContext.Response.Body, Encoding.UTF8, defaultBufferSize, ArrayPool<byte>.Shared, ArrayPool<char>.Shared);
@@ -99,7 +99,7 @@ private async Task OnNavigateTo(string uri)
         }
         else
         {
-            _httpContext.Response.Redirect(uri);
+            await HandleNavigationBeforeResponseStarted(_httpContext, uri);
         }
         SignalRendererToFinishRendering();
     }

src/Components/Endpoints/src/Rendering/EndpointHtmlRenderer.Prerendering.cs

@@ -206,20 +206,28 @@ public static ValueTask<PrerenderedComponentHtmlContent> HandleNavigationExcepti
                 "response and avoid using features like FlushAsync() before all components on the page have been rendered to prevent failed navigation commands.",
                 navigationException);
         }
-        else if (IsPossibleExternalDestination(httpContext.Request, navigationException.Location)
+        else
+        {
+            return HandleNavigationBeforeResponseStarted(httpContext, navigationException.Location);
+        }
+    }
+
+    private static ValueTask<PrerenderedComponentHtmlContent> HandleNavigationBeforeResponseStarted(HttpContext httpContext, string destinationLocation)
+    {
+        if (IsPossibleExternalDestination(httpContext.Request, destinationLocation)
             && IsProgressivelyEnhancedNavigation(httpContext.Request))
         {
             // For progressively-enhanced nav, we prefer to use opaque redirections for external URLs rather than
             // forcing the request to be retried, since that allows post-redirect-get to work, plus avoids a
             // duplicated request. The client can't rely on receiving this header, though, since non-Blazor endpoints
             // wouldn't return it.
             httpContext.Response.Headers.Add("blazor-enhanced-nav-redirect-location",
-                OpaqueRedirection.CreateProtectedRedirectionUrl(httpContext, navigationException.Location));
+                OpaqueRedirection.CreateProtectedRedirectionUrl(httpContext, destinationLocation));
             return new ValueTask<PrerenderedComponentHtmlContent>(PrerenderedComponentHtmlContent.Empty);
         }
         else
         {
-            httpContext.Response.Redirect(navigationException.Location);
+            httpContext.Response.Redirect(destinationLocation);
             return new ValueTask<PrerenderedComponentHtmlContent>(PrerenderedComponentHtmlContent.Empty);
         }
     }